Support gzip-compressed gRPC response messages

[ryanfowler]

Summary

• Added gRPC message encoding handling that reads grpc-encoding, decompresses gzip-framed messages before protobuf decoding, and reports unsupported encodings by name
• Advertises grpc-accept-encoding: gzip for gRPC calls and reflection so servers can safely return compressed messages
• Updated streaming, schema-aware, and reflection response paths to decode compressed frames consistently
• Documented the behavior and added integration coverage for gzip responses, unsupported encodings, and the new request header

Testing

• cargo fmt
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo test --all-features --test integration -- --test-threads=1